If you are a linux user or a linux system admin or you are working in a production environment then you have to know about the software disk management and all the methods to provide flexblibity in storage management.In storage management you must have indepth knowledge of lvm.But before lvm you must have sound knowledge of volume group.

This is a detail tutorial on linux volume group.Everything we mentioned here in this article will be directly or indirectly related with Linux Volume Group.We will learn how to manage Storage Device concerned with volume group using command line.vgcreate vgremove vgchange vgconvert vgreduce vgextend vgmerge vgsplit and vgrename  are those linux command on which we are going to discuss in detail inside this tutorial.

First we need to create Physical Volumes that will be used to create Volume Group.

 [root@localhost ~]# pvcreate /dev/hda{6,7,8}
  Physical volume "/dev/hda6" successfully created
  Physical volume "/dev/hda7" successfully created
  Physical volume "/dev/hda8" successfully created

To check whether physical Volumes have been created or not use pvscan command.

 [root@localhost ~]# pvscan
  PV /dev/hda6                      lvm2 [482.83 MB]
  PV /dev/hda7                      lvm2 [862.84 MB]
  PV /dev/hda8                      lvm2 [1.13 GB]
  Total: 3 [2.44 GB] / in use: 0 [0   ] / in no VG: 3 [2.44 GB]

Then we create Volume Group named vg00.

 [root@localhost ~]# vgcreate vg00 /dev/hda{6,7,8}
  Volume group "vg00" successfully created

 [root@localhost ~]# vgs
  VG   #PV #LV #SN Attr   VSize VFree
  vg00   3   0   0 wz--n- 2.43G 2.43G

 [root@localhost ~]# pvscan
  PV /dev/hda6   VG vg00   lvm2 [480.00 MB / 480.00 MB free]
  PV /dev/hda7   VG vg00   lvm2 [860.00 MB / 860.00 MB free]
  PV /dev/hda8   VG vg00   lvm2 [1.12 GB / 1.12 GB free]
  Total: 3 [2.43 GB] / in use: 3 [2.43 GB] / in no VG: 0 [0   ]

 [root@localhost ~]# vgdisplay
  --- Volume group ---
  VG Name               vg00
  System ID             
  Format                lvm2
  Metadata Areas        3
  Metadata Sequence No  1
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                0
  Open LV               0
  Max PV                0
  Cur PV                3
  Act PV                3
  VG Size               2.43 GB
  PE Size               4.00 MB
  Total PE              623
  Alloc PE / Size       0 / 0   
  Free  PE / Size       623 / 2.43 GB
  VG UUID               7rDn7R-vnAv-aFQv-XlrP-CDha-h2tz-sNptkj

Learn how to limit maximum number logical volumes of volume group using "vgchange command"

 [root@localhost ~]# vgchange -l 110 /dev/vg00
  Volume group "vg00" successfully changed

Now using vgdisplay command you can check the maximum number of logical volumes allowed in this group. just see "MAX LV 110" in below output.

 [root@localhost ~]# vgdisplay
  --- Volume group ---
  VG Name               vg00
  System ID             
  Format                lvm2
  Metadata Areas        3
  Metadata Sequence No  2
  VG Access             read/write
  VG Status             resizable
  MAX LV                110
  Cur LV                0
  Open LV               0
  Max PV                0
  Cur PV                3
  Act PV                3
  VG Size               2.43 GB
  PE Size               4.00 MB
  Total PE              623
  Alloc PE / Size       0 / 0   
  Free  PE / Size       623 / 2.43 GB
  VG UUID               7rDn7R-vnAv-aFQv-XlrP-CDha-h2tz-sNptkj

How to remove a physical Volume from a Volume Group using "vgreduce " command.

 [root@localhost ~]# pvscan
  PV /dev/hda6   VG vg00   lvm2 [480.00 MB / 480.00 MB free]
  PV /dev/hda7   VG vg00   lvm2 [860.00 MB / 860.00 MB free]
  PV /dev/hda8   VG vg00   lvm2 [1.12 GB / 1.12 GB free]
  Total: 3 [2.43 GB] / in use: 3 [2.43 GB] / in no VG: 0 [0   ]

Now I am going to remove "/dev/hda6" physical Volume from Volume Group vg00 here.

 [root@localhost ~]# vgreduce vg00 /dev/hda6
  Removed "/dev/hda6" from volume group "vg00"

Now you can check whether physical volume /dev/hda6 has been removed or not by using pvscan command.

 [root@localhost ~]# pvscan
  PV /dev/hda7   VG vg00            lvm2 [860.00 MB / 860.00 MB free]
  PV /dev/hda8   VG vg00            lvm2 [1.12 GB / 1.12 GB free]
  PV /dev/hda6                      lvm2 [482.83 MB]
  Total: 3 [2.44 GB] / in use: 2 [1.96 GB] / in no VG: 1 [482.83 MB]

Now you can very clearly see that Physical Volume /dev/hda6 is now not the part of Volume Group vg00.

How to add a physical volume to a Volume Group using "vgextend" command.

Now I want to add a new physical Volume /dev/hda9 to my existing volume group vg00.

Lets have a look of your volume group detail before adding any new physical volume.

 [root@localhost ~]# pvscan
  PV /dev/hda7   VG vg00            lvm2 [860.00 MB / 860.00 MB free]
  PV /dev/hda8   VG vg00            lvm2 [1.12 GB / 1.12 GB free]
  PV /dev/hda6                      lvm2 [482.83 MB]
  PV /dev/hda9                      lvm2 [964.81 MB]
  Total: 4 [3.38 GB] / in use: 2 [1.96 GB] / in no VG: 2 [1.41 GB]

 [root@localhost ~]# vgs
  VG   #PV #LV #SN Attr   VSize VFree
  vg00   2   0   0 wz--n- 1.96G 1.96G

Now I am going to add new physical Volume /dev/hda9 to volume group vg00.

 [root@localhost ~]# vgextend vg00 /dev/hda9
  Volume group "vg00" successfully extended

Now Check Volume Group details after adding new physical volume to it.

 [root@localhost ~]# vgs
  VG   #PV #LV #SN Attr   VSize VFree
  vg00   3   0   0 wz--n- 2.91G 2.91G

How to split a physical volume of a volume group using "vgsplit" command.

before splitting volume group vg00 lets have a look about volume group.

 [root@localhost ~]# vgs
  VG   #PV #LV #SN Attr   VSize VFree
  vg00   3   0   0 wz--n- 2.91G 2.91G

 [root@localhost ~]# pvscan
  PV /dev/hda7   VG vg00            lvm2 [860.00 MB / 860.00 MB free]
  PV /dev/hda8   VG vg00            lvm2 [1.12 GB / 1.12 GB free]
  PV /dev/hda9   VG vg00            lvm2 [964.00 MB / 964.00 MB free]
  PV /dev/hda6                      lvm2 [482.83 MB]
  Total: 4 [3.38 GB] / in use: 3 [2.91 GB] / in no VG: 1 [482.83 MB]

Now you can clearly see we have only one volume group present here named vg00 of size 2.91GB. Now i am going to splitt this volume group vg00 using vgsplit command.

 [root@localhost ~]# vgsplit vg00 vg11 /dev/hda7
  New volume group "vg11" successfully split from "vg00"

Now see the volume group detail after splitting volume group to confirm your successful splitting.

 [root@localhost ~]# vgs
  VG   #PV #LV #SN Attr   VSize   VFree  
  vg00   2   0   0 wz--n-   2.07G   2.07G
  vg11   1   0   0 wz--n- 860.00M 860.00M

Now you can clearly see there are two volume groups now vg00 and vg11.

 [root@localhost ~]# pvscan
  PV /dev/hda8   VG vg00            lvm2 [1.12 GB / 1.12 GB free]
  PV /dev/hda9   VG vg00            lvm2 [964.00 MB / 964.00 MB free]
  PV /dev/hda7   VG vg11            lvm2 [860.00 MB / 860.00 MB free]
  PV /dev/hda6                      lvm2 [482.83 MB]
  Total: 4 [3.38 GB] / in use: 3 [2.91 GB] / in no VG: 1 [482.83 MB]

You can clearly see that two volume group vg00 and vg11 where vg00 consist of /dev/hda8 and /dev/hda9 and vg11 consist of /dev/hda7.

NOTE: It is not possible to split logical volumes between volume groups.vgsplit only moves complete physical volume.

Now question arises that what to do when we want to move a part of physical volume?

Answer is very simple, just use pvmove command if you want to move a part of physical volume.

How to combine two volume group using vgmerge "command".

In above pvscan output you can clearly see there are two volume group now "vg00" and "vg11".Now what i want to do is to combine or you can say merge these two volume groups together.So lets see how we can combine or merge these two volume groups using "vgmerge" command.

 [root@localhost ~]# vgmerge -v vg00 vg11
    Checking for volume group "vg00"
    Checking for volume group "vg11"
    Archiving volume group "vg11" metadata (seqno 2).
    Archiving volume group "vg00" metadata (seqno 5).
    Writing out updated volume group
    Creating volume group backup "/etc/lvm/backup/vg00" (seqno 6).
  Volume group "vg11" successfully merged into "vg00"

Now you can check volume group status or volume group information for your confirmation using vgs command or vgdisplay command or pvscan command.

 [root@localhost ~]# vgs
  VG   #PV #LV #SN Attr   VSize VFree
  vg00   3   0   0 wz--n- 2.91G 2.91G

[root@localhost ~]# pvscan
  PV /dev/hda8   VG vg00            lvm2 [1.12 GB / 1.12 GB free]
  PV /dev/hda9   VG vg00            lvm2 [964.00 MB / 964.00 MB free]
  PV /dev/hda7   VG vg00            lvm2 [860.00 MB / 860.00 MB free]
  PV /dev/hda6                      lvm2 [482.83 MB]
  Total: 4 [3.38 GB] / in use: 3 [2.91 GB] / in no VG: 1 [482.83 MB]

How to rename a volume group using "vgrename" command.

Now here i am going to show you how to rename a volume group using vgrename command.

For example i am going to rename volume group vg00 to shivangi.

 [root@localhost ~]# vgrename /dev/vg00 /dev/shivangi
  Volume group "vg00" successfully renamed to "shivangi"

For your confirmation check volume group info using vgs or pvscan command.

 [root@localhost ~]# vgs
  VG       #PV #LV #SN Attr   VSize VFree
  shivangi   3   0   0 wz--n- 2.91G 2.91G

 [root@localhost ~]# pvscan
  PV /dev/hda8   VG shivangi        lvm2 [1.12 GB / 1.12 GB free]
  PV /dev/hda9   VG shivangi        lvm2 [964.00 MB / 964.00 MB free]
  PV /dev/hda7   VG shivangi        lvm2 [860.00 MB / 860.00 MB free]
  PV /dev/hda6                      lvm2 [482.83 MB]
  Total: 4 [3.38 GB] / in use: 3 [2.91 GB] / in no VG: 1 [482.83 MB]

How to convert lvm1 to lvm2 using "vgconvert"

 [root@localhost ~]# vgconvert -M2 shivangi
  Volume group "shivangi" already uses format lvm2

since i am already using lvm version 2 thats why you can see the above output.

Now How to convert lvm2 to lvm1.

How to Degrade LVM Version.

 
[root@localhost ~]# vgconvert -M1 shivangi
  Volume group shivangi successfully converted

For confirmation you can check it using pvscan command.

 [root@localhost ~]# pvscan
  PV /dev/hda7   VG shivangi        lvm1 [860.00 MB / 860.00 MB free]
  PV /dev/hda8   VG shivangi        lvm1 [1.12 GB / 1.12 GB free]
  PV /dev/hda9   VG shivangi        lvm1 [964.00 MB / 964.00 MB free]
  PV /dev/hda6                      lvm2 [482.83 MB]
  Total: 4 [3.38 GB] / in use: 3 [2.91 GB] / in no VG: 1 [482.83 MB]

So now you can clearly see here lvm version is 1 showing as lvm1.

You can also convert lvm version 1 back to lvm version 2 using vgconvert command.

 [root@localhost ~]# vgconvert -M2 shivangi
  Volume group shivangi successfully converted

For confirmation check it again using pvscan.

 [root@localhost ~]# pvscan
  PV /dev/hda7   VG shivangi        lvm2 [860.00 MB / 860.00 MB free]
  PV /dev/hda8   VG shivangi        lvm2 [1.12 GB / 1.12 GB free]
  PV /dev/hda9   VG shivangi        lvm2 [964.00 MB / 964.00 MB free]
  PV /dev/hda6                      lvm2 [482.83 MB]
  Total: 4 [3.38 GB] / in use: 3 [2.91 GB] / in no VG: 1 [482.83 MB]

Hence you can see it is converted back to lvm version2.

You can also read our article:

The Advance Guide To LVM Part-1.

LVM on Top of RAID.

How to Create RAID on LOOP DEVICES and LVM over RAID.